Naturally occurring clays such as dioctahedral smectites are composed of semicrystalline aluminosilicate layers (lamellae) held together by Van der Waals and electrostatic forces. Anionic charges on the siliceous layers are neutralized by cations in the interlamellar spaces. These cations are usually sodium, calcium, or potassium. When these cations are large oligomers of inorganic cations such as Fe.sup.+3, Cr.sup.+3 or when they are metal hydroxy polymer cations such as (Al.sub.13 O.sub.4 (OH).sub.24 (H.sub.2 O).sub.12).sup.7+ or (Zr(OH).sub.2.4H.sub.2 O).sub.4.sup.8+, they act as pillars, propping the clay layers apart to afford a pillared layered clay. Upon heating, these oligomers or polymers are converted to the metal oxide, thus preventing the collapse of the clay layers and thus pillaring the clay.
These smectite clays are known to catalyze reactions such as alkylation, cracking, ester formation, dimerization, oligomerization, etc. However, because the naturally occurring clays have a large variation in impurity content, industrial demand for the natural smectites has been very limited. Therefore, attempts have been made to synthesize some of these smectite clays. For example, European Patent Application 163560 discloses a method of preparing a beidellite clay (one of the smectite clays). The process involves taking a mixture containing aluminum nitrate, tetraethylorthosilicate (TEOS), sodium carbonate and sodium hydroxide, drying the mixture and then calcining to give aluminum oxide, silicon oxide, and sodium oxide, adding to that hydroxide anions and heating the resultant slurry to a temperature of about 340.degree. C. for 14 days. Although this method produces a beidellite that is purer than the naturally occurring beidellite, the use of oxides leads to incomplete reaction even though the synthesis is carried out at high temperatures. Additionally, the presence of sodium is detrimental to the catalysis of certain reactions and therefore, the sodium has to be replaced by some other cation.
Applicant has solved the problems with the synthesis of beidellite found in the prior art by using a reaction mixture which contains a secondary or tertiary amine, a quaternary ammonium salt or a quaternary phosphonium salt along with reactive sources of aluminum and silicon. For example, tetramethylammonium hydroxide is mixed with alumina and colloidal silica along with water at a pH of about 8.5 to about 14 and reacted at a temperature of 150.degree.-210.degree. C. for about 1 to 20 days to provide a TMA.sup.+ -beidellite. The resultant product is also unique in that unlike the beidellites which are described in the prior art, the instant product has crystals whose average crystallite size is about 50-150 Angstroms, has a surface area of at least 80 m.sup.2 /g, is substantially free of sodium cations and has its 060 X-ray diffraction peak at a d-spacing of 1.50 Angstroms. The tetramethylammonium cations have taken the place of sodium cations that are present in prior art beidellite products. Although the prior art shows that a sodium beidellite can be exchanged with an alkyl ammonium compound the resultant exchange product does not have the same characteristics as the instant composition.
Although the prior art shows that quaternary ammonium compounds can be used to prepare some synthetic clays, there is no indication that an amine, a quaternary ammonium compound or a quaternary phosphonium compound could be used to prepare a synthetic beidellite. For example, R. M. Barrer and L. W. R. Dicks in J. Chem. Soc. (A), 1967, 1523-1529, have shown that alkyl ammonium compounds can be used to synthesize montmorillonites and hectorites. Thus, applicant is the first to synthesize an alkyl ammonium beidellite having small crystallites, a large surface area and its 060 peak at a d-spacing of 1.50 Angstroms.